1. Field of the Invention
This invention relates to a non-aqueous electrolyte cell, comprised of a cell element accommodated in an exterior packaging material formed by a laminated film, and a manufacturing method therefor. More particularly, it relates to improvement in mounting position accuracy of electrode terminal leads.
2. Description of the Related Art
In a lithium ion polymer cell, employing an ion conductive polymer as an electrolyte, an electrolyte which is solid or gelated at ambient temperature, heat evolution or ignition is retarded significantly against rise in the internal temperature, internal shorting or shorting under an external pressure, such that measures for structural safety deemed to be necessary due to use in the conventional solution type lithium ion cells of the petroleum based liquid electrolyte, namely    a) a gasket and caulking structure required for sealing the cell in a metal can which is a pressure vessel,    b) a cleavage valve structure for evading the risk on rise in the internal pressure,    c) a structure of thermally disconnecting external terminals on rise in the internal temperature, or    d) a structure of raising the electric resistance across terminals on rise in the internal temperaturebecome unnecessary such that the basic structure inclusive of an external packaging can possibly be simplified, thus assuring satisfactory external packaging on heat sealing an aluminum laminate film and shielding off the moisture even in the absence of special safety structures within the inside of the cell.
However, if this structure is actually used, positive and negative electrode plates need to be punched to the shape of a rectangle with exposed metal foil portions used for welding a lead plate, the positive and negative electrode plates being then arranged facing each other without overlapping of the exposed metal foil portions, to provide an assembly of the positive and negative electrode plates. A large number of such assemblies then are stacked together to complete a cell unit. In such structure, the surface of each positive electrode plate coated with an active material is set so as to be smaller in area than the surface of each negative electrode plate coated with an active material. In order to prevent possible contact of the exposed metal foil portion of the positive electrode with the negative electrode surface and consequent internal shorting, the portion of the exposed positive electrode foil portion overlapped with the negative electrode surface is coated with an insulating tape.
Also, a large number of positive electrode terminals and the negative electrode terminals, exposed on the lateral sides, are collected together to form external terminals. To this end, separate tab terminals are collectively welded on the overlapped exposed metal foil surfaces to form external terminals, over which laminated aluminum films are set to form a trim external cell package. However, with this method, it is necessary to put positive and negative electrodes alternately to form a cell unit, to weld separate tab terminals to provide external terminals, and to effect heat sealing of aluminum laminate films such as to evade welding margins, otherwise the welded portions of the positive and negative external terminals punch through the insulating layers of the inner wall sections of the aluminum laminate films to produce internal shorting through the aluminum laminate film. Since the cell suffering such internal shorting is discarded as a reject, the heat sealing needs to be performed such as to evade the welding margins, as mentioned above.
In such cell, the magnitude of the volumetric energy density, representing the cell capacity per a cell volume calculated from the maximum sizes in the length, width and height of the outer profile of the cell is diminished. Specifically, due to    a) dimensional loss caused by punching electrode plates to rectangular shape so that the positive electrode will be smaller than the negative electrode,    b) dimensional loss caused by protecting the exposed metal foil portion of the positive electrode against contact with the negative electrode, and    c) dimensional loss caused by heat-sealing such as to evade welded portions of bundled exposed metal foil portions of the positive and negative electrodes to external terminals,
the merit of the simpler external structure is not translated into capacity increase per volume.
On the other hand, if a cell employing an ion conductive polymer is to be constructed by wrapping an elongated positive terminal plate and an elongated negative terminal plate, the conventional practice is to wrap an electrode material, free of a portion not coated with an active material or a lead, to sever both electrodes to suitable lengths and to remove the ion conductive polymer and the active material on the outer side to weld the lead subsequently.
However, with the above structure, the process of wrapping an elongated electrode, severing the electrode to a suitable length and providing an exposed metal foil portion at an electrode end of each of the positive and negative electrodes disposed on the outer ends to weld the lead in position, is required, thus obstructing designing of a continuous production process. Moreover, in this process, part of the removed material tends to be entwined in the cell unit to precipitate an extraneous metal or to cause internal shorting.
In wrapping elongated positive and negative electrode plates, such a method has been proposed in which a portion not coated with an active material or with a polymer electrolyte is provided in an outer rim portion of the electrode plate, and one or both of the electrodes or both tab terminals are mounted in position before proceeding to wrapping. This structure is used in general in a square type version of the liquid-based lithium ion cell.
However, with the above structure, the position of the leads provided on the electrodes at the outer end is not constant, at the wrapping end, due to variations in thickness of the active material or to variations in thickness of the ion conductive polymer. In an extreme case, when an external packaging material is applied, the positive and negative terminals are superposed to produce shorting. Therefore, an extremely high degree of accuracy is required in connection with thickness variations of the active material and the polymer electrolyte, thus unnecessarily raising equipment cost and lowering the production yield.